Luminescence and energy transfer performances of Tb3+/Mn4+ co-doped Sr2LuTaO6 double-perovskite phosphors for a highly sensitive optical thermometer

A series of Tb3+/Mn4+ co-doped double-perovskite oxides Sr2LuTaO6 (SLT) phosphors are synthesized by a solid-state method. The results of structural characterization prove that the Tb3+ and Mn4+ ions are successfully doped into the SLT host. The photoluminescence excitation (PLE) and photoluminescence (PL) spectra of Sr2LuTaO6:Tb3+, Sr2LuTaO6:Mn4+ and Sr2LuTaO6:Tb3+/Mn4+ are illustrated in detail. Under ultraviolet (UV) excitation, bright green and red lights are obtained from the Sr2LuTaO6:Tb3+/Mn4+ phosphor. In particular, the emission intensity of Tb3+ ions in Sr2LuTaO6:Tb3+/Mn4+ is enhanced by the energy transfer (ET) process from Mn4+ to Tb3+. The thermal enhancement of Tb3+ ion radiation in Sr2LuTaO6: Tb3+/Mn4+ also proves the ET process (Mn4+ -> Tb3+). In addition, the thermal enhancement of Tb3+ ion radiation and the thermal quenching of Mn4+ ion radiation in the Sr2LuTaO6:Tb3+/Mn4+ system can be applied to develop optical thermometry based on luminescence intensity ratio (LIR) technology. Therefore, the LIRs of Mn4+ (E-2(g) -> (4)A(2g)) and Tb3+ (D-5(4) -> F-7(5,4)) are investigated in the temperature range from 313 to 573 K. The absolute sensitivity (Sa) and relative sensitivity (Sr) of the Sr2LuTaO6:Tb3+/Mn4+ phosphor are calculated. The maximum values of Sa and Sr are obtained from the LIR of Tb3+: D-5(4) -> F-7(4) (570-599 nm) and Mn4+: E-2(g) -> (4)A(2g) (625-705 nm). The maximum Sa is 10.18% K-1 at 543 K, and the maximum value of Sr reaches 1.98% K-1 at 543 K. These results confirm that the ET process from Mn4+ to Tb3+ contributes to increasing the temperature measuring sensitivity of the Sr2LuTaO6:Tb3+/Mn4+ phosphor. Therefore, the Sr2LuTaO6:Mn4+/Tb3+ phosphor has prospective potential in optical thermometry and provides advantageous guidance for designing high-sensitivity optical thermometers.

Automated summary

Tb3+/Mn4+ co-doped Sr2LuTaO6 phosphors were successfully synthesized by a solid-state method. Under UV excitation, the phosphors exhibited bright green and red lights. The energy transfer from Mn4+ to Tb3+ enhanced the emission intensity of Tb3+ ions. Furthermore, the phosphors showed potential for optical thermometry based on luminescence intensity ratio technology.